The advantages of synthesizing insulation coatings for magnet wire from aromatic dianhydride and aromatic diamine materials are known in the prior art. The techniques for such synthesis, however, have not always yielded consistent reaction product materials. Moreover, the starting materials comprised of the aromatic dianhydrides and aromatic diamines, as well as the polyamic acid produced therefrom are apt to be difficult to store and require solvent materials which are expensive and generally are dangerous pollutants which must be disposed of during the coating process. Until recently, the polymeric materials exhibited such water sensitivity that they were considered to be generally nonstorable for any significant period of time. One solution now available for that particular problem is disclosed in my copending application titled, "Improved Process for Producing Coating Materials," U.S. application Ser. No. 803,037, filed Feb. 27, 1969, now abandoned, and invented by Marvin A. Peterson, which is assigned to the same assignee as the present invention.
It is known, that for magnet wire insulation purposes, or surface coatings in general, superior coatings are obtained by utilizing the highest possible molecular weight of polymer and by utilizing polymers which are characterized by consistent and uniform molecular weights. When low molecular weight entities are present, they are generally lost during the cure.
A further technical problem which has proved difficult to solve, entails the necessity for obtaining a preferred viscosity and solids/solvent ratio of the coating material solution at the time it is applied to the magnet wire. These parameters of wire coating operation have proven difficult to control and even more difficult to optimize for a given wire coating operation in order to achieve both ideal coating rate of application and a superior enamel insulation in the finished product. Presently known coating compositions cannot be generally relied upon to provide consistently the functional and compositional requirements for wire coating operation as well as a satisfactory insulation coating.